The present invention concerns a novel apparatus and process for communicating an electrogram from a patient. This application is related to U.S. patent application Ser. No. 514,514, filed July 18, 1983 and entitled "Analog Telemetry System For Biomedical Implant."
In U.S. Pat. No. 4,361,153, issued Nov. 30, 1982 and assigned to the assignee of the present invention, there is disclosed the use of a resonant impedance modulated transponder, in a device implanted in the patient, to modulate the phase of a relected magnetic signal that is the product of a magnetic carrier imposed from outside of the body. In this manner, information is transmitted from a fixed internal implant to a positionable external telemetry unit. A relatively high energy magnetic field at a carrier frequency is established by a transmitter in the external unit. The field permates the skin, underlying tissue and case of the implant and induces a signal in a resonant, impedance modulated transponder in the implant tuned to the carrier frequency. A second field is reradiated or reflected at the carrier frequency by the resonant transponder. The transponder's impedance is varied in accordance with a modulation input signal, causing a shift in the phase angle and amplitude of the transponder's contribution to the composite reflected signal, thereby resulting in a proportional phase and amplitube shift in the composite reflected signal. The composite reflected signal is picked up and demodulated by a phase shift detector in the external telemetry unit.
In the primary embodiment disclosed in U.S. Pat. No. 4,361,153, the modulation input signal is a pulse width modulated binary signal that is generated by the implant. The patent also discloses that the modulation input signal may be an analog input signal.
It has been found that a resonant impedance modulated transponder in an implant can be utilized in connection with communicating an electrogram from a patient. It has been discovered that such communication can be effective utilizing an analog representation of the electrogram, such as the analog amplified electrogram signal itself. In this manner, the necessity for digitizing an analog signal and providing a pulse width modulated binary signal is obviated. Systems in which the analog signal must be digitized require an analog to digital converter and also a subsequent digital to analog converter, but in accordance with the present invention a system is provided in which such converters are unnecessary to achieve the desired result.
It is an object of the present invention to provide an apparatus and process for communicating an electrogram from a patient, in a manner that is accurate and efficient and results in an electrogram signal outside of the body that corresponds as close as possible to the patient's electrogram.
Another object of the present invention is to provide apparatus for communicating an electrogram from a patient, which uses a minimum amount of parts in the implant yet produces a high quality EKG.
A further object of the present invention is to provide an apparatus and process for communicating more than one waveform at a time from a patient.
A still further object of the present invention is to provide an apparatus and process for communicating an electrogram from a patient, which is simple in construction and easy to manufacture.
Other objects and advantages will become apparent as the description proceeds.